1. Field of the Invention
The present invention is generally related to an image processing system, and more particularly to an image processing system for processing an image processed by run-lengths.
2. Description of the Related Art
In a image transmission apparatus, such as a facsimile machine, image signals read by an image sensor are converted into binary data, the binary data is coded in accordance with a coding method, such as an MH (Modified Huffman) method or an MR (Modified Read) method, and the coded data is transmitted to a receiver via a communication line. In the receiver, the coded data is decoded into a binary image data, and an original image is reproduced from the binary data and recorded on a recording medium (e.g. a recording paper).
A conventional image processing unit is formed, for example, as shown in FIG.1. Referring to FIG. 1, an image processing unit has a CPU 50, a memory 51, a coder/decoder 52, a magnification processing unit 53 and an interface circuit 54 all of which are connected to each other by a system bus. The coder/decoder 52 codes binary data into a code (e.g. the MH code or MR code), and decodes the code into binary data. The magnification processing unit 53 processes binary data so that an image size is changed. The interface circuit 54 is coupled to a printer, a transmitter unit, and a receiver unit in a facsimile.
In a case where a size of an original in the transmitter differs from a size of a recording paper on which an original image should be recorded, the magnification processing unit 53 of transmitter carries out a process in which a size of an image represented by the binary data is changed so that the image can be recorded on the recording paper in the receiver. This process is referred to as a size changing process or a pixel (picture element) density conversion process. In a conventional facsimile machine, a reducing process of an image is, as the pixel density conversion process, mainly performed. Reducing processes in accordance with a logical sum method and a thinning out method have been proposed. However, lines of character images processed by the conventional reducing process are not clear or cut, so that the quality of an image deteriorates.
To eliminate the above disadvantages, a method for converting a pixel density in a run-length domain has been proposed (Electronics and Communication Society Technical Report IE79-60 pp9-14). However, since, in this method, a computing of all input run-lengths must be carried out, amount of computing becomes large.
It has been known that each MH code processed in a facsimile machine is formed of a Terminating code in a case where a run-length represented by each MH code is in a range from 0 to 63, and is formed of Make up code and Terminating code in a case where a run-length represented by each MH code is in a range from 64 to 2560. Thus, 16 bits are needed to process each run-length, so that a size of a memory used to convert the pixel density in the run-length domain becomes large. Furthermore, the run-length data is not an appropriate size for a digital processing unit in which data is processed byte by byte.